Makefile.inc: Generate master header and pointer as C structs

The makefiles don't like cbfs file names with spaces in them so update
the file name with '_' instead of spaces. To keep the master header at
the top of cbfs, add a placeholder.

This removes the need to handle the cbfs master header in cbfstool.
This functionality will be dropped in a later CL.

On x86 reserve some space in the linker script to add the pointer.
On non-x86 generate a pointer inside a C struct file.

As a bonus this would actually fix the master header pointer mechanism
on Intel/APL as only the bootblock inside IFWI gets memory mapped.

TESTED on thinkpad X201: SeaBIOS correctly finds the cbfs master
header.

Change-Id: I3ba01be7da1f09a8cac287751497c18cda97d293
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59132
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/lib/cbfs_master_header.c

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <endian.h>
+#include <fmap_config.h>
+#include <commonlib/bsd/cbfs_serialized.h>
+
+struct cbfs_header header = {
+	.magic = cpu_to_be32(CBFS_HEADER_MAGIC),
+	.version = cpu_to_be32(CBFS_HEADER_VERSION),
+	/*
+	 * The offset and romsize fields within the master header are absolute
+	 * values within the boot media. As such, romsize needs to reflect
+	 * the end 'offset' for a CBFS. To achieve that the current buffer
+	 * representing the CBFS region's size is added to the offset of
+	 * the region within a larger image.
+	 */
+	.romsize = cpu_to_be32(FMAP_SECTION_COREBOOT_START + FMAP_SECTION_COREBOOT_SIZE
+			       - FMAP_SECTION_FLASH_START),
+	/*
+	 * The 4 bytes are left out for two reasons:
+	 * 1. the cbfs master header pointer resides there
+	 * 2. some cbfs implementations assume that an image that resides
+	 *    below 4GB has a bootblock and get confused when the end of the
+	 *    image is at 4GB == 0.
+	 */
+	.bootblocksize = cpu_to_be32(4),
+	.align = cpu_to_be32(CBFS_ALIGNMENT),
+	.offset = cpu_to_be32(FMAP_SECTION_COREBOOT_START - FMAP_SECTION_FLASH_START),
+	.architecture = cpu_to_be32(CBFS_ARCHITECTURE_UNKNOWN),
+};